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Bryozoans are common commensal on hard surfaces and cover slow-moving animals like molluscans, sea turtles, brachyuran crabs, and horseshoe crabs. A total of six species of bryozoans belonging to four genus under three families of order Cheilostomatida were recorded encrusting on the carapaces of horseshoe crabs collected from Indian Sundarbans along the east coast of India and two among them, viz., Biflustra savartii (Audouin, 1826) and Sinoflustra arabianensis (Menon & Nair, 1975) are reported for the first time. Additionally, Jellyella tuberculata (Bosc, 1802) is reported for the first time from West Bengal coastal waters, previously known only from the Odisha coast of India. Both male and female horseshoe crabs were found to have been encrusted with bryozoan mats, although adequately not known about the life stages of their encrustation.

Xiphosura, the so-called horseshoe crabs, are a group of extant marine chelicerates that have a fossil record extending back to the Lower Ordovician. Their temporal range, coupled with a supposed record of bradytelic evolution has made them a focus of palaeontological consideration for over two centuries. As such, there are an array of taxa erected during the 20th century that have remained unexamined in light of new material and revised phylogenetic theories. Stem xiphosurids in particular require further research to uncover the diversity and disparity of non-crown group horseshoe crabs. To align with the recent increase in mid to late Paleozoic horseshoe crab research, we reconsider the stem xiphosurids “Kasibelinurus” randalli and “Bellinurus” alleganyensis from the Late Devonian of Pennsylvania and New York State. We conclude that they are synonyms and belong in neither Kasibelinurus nor Bellinurus, and the new genus, Patesia, is erected to accommodate them. Reconsidering stem xiphosurids highlights that particularly in the Late Devonian there was a high disparity of form. One such stem xiphosurid may represent the morphological stock that gave rise to the Carboniferous taxa and the first xiphosurid radiation.

The central nervous system (CNS) presents unique insight into the behaviors and ecology of extant and extinct animal groups. However, neurological tissues are delicate and prone to rapid decay, and thus their occurrence as fossils is mostly confined to Cambrian Burgess Shale–type deposits and Cenozoic amber inclusions. We describe an exceptionally preserved CNS in the horseshoe crab Euproops danae from the late Carboniferous (Moscovian) Mazon Creek Konservat-Lagerstätte in Illinois, USA. The E. danae CNS demonstrates that the general prosomal synganglion organization has remained essentially unchanged in horseshoe crabs for >300 m.y., despite substantial morphological and ecological diversification in that time. Furthermore, it reveals that the euarthropod CNS can be preserved by molding in siderite and suggests that further examples may be present in the Mazon Creek fauna. This discovery fills a significant temporal gap in the fossil record of euarthropod CNSs and expands the taphonomic scope for preservation of detailed paleoneuroanatomical data in the Paleozoic to siderite concretion Lagerstätten of marginal marine deposits.

Impending anthropogenic climate change will severely impact coastal organisms at unprecedented speed. Knowledge on organisms’ evolutionary responses to past sea‐level fluctuations and estimation of their evolutionary potential is therefore indispensable in efforts to mitigate the effects of future climate change. We sampled tens of thousands of genomic markers of ~300 individuals in two of the four extant horseshoe crab species across the complex archipelagic Singapore Straits. Carcinoscorpius rotundicauda Latreille, a less mobile mangrove species, has finer population structure and lower genetic diversity compared with the dispersive deep‐sea Tachypleus gigas Müller. Even though the source populations of both species during the last glacial maximum exhibited comparable effective population sizes, the less dispersive C. rotundicauda seems to lose genetic diversity much more quickly because of population fragmentation. Contra previous studies’ results, we predict that the more commonly sighted C. rotundicauda faces a more uncertain conservation plight, with a continuing loss in evolutionary potential and higher vulnerability to future climate change. Our study provides important genomic baseline data for the redirection of conservation measures in the face of climate change and can be used as a blueprint for assessment and mitigation of the adverse effects of impending sea‐level rise in other systems.

Horseshoe crabs may act as mobile substrata for communities of sessile marine organisms on intertidal mudflats. In Singapore, the mangrove horseshoe crabs, Carcinoscorpius rotundicauda (Latreille, ...

The capacity of organisms to change their sex has evolved independently in several species. Sex change has been widely studied, but research approaches have differed and conclusions have often been specific. Although sex allocation theory provides a unifying framework for the study of sex change, this unity has not always been appreciated, Environmental sex reversal (ESR), which results in a mismatch between genotypic and phenotypic sex, is well documented in numerous species and may be induced by chemical exposure. In the present study, an attempt was made to hypothesize the phenomenon of sex reversal in both Asian species (Tachypleus gigas and Carcinoscorpius rotundicauda) of the horseshoe crab in accordance with the size of the animals. Our findings suggest that both Asian species of horseshoe crabs ultimately show a positive sign of sex reversal phenomenon, however, this hypothesis needs further confirmation by studying the hormonal changes at all moulting stages of the horseshoe crab

For animal embryos that develop externally, the physio-chemical environment can substantially affect offspring viability. In the case of the American horseshoe crab (Limulus polyphemus), se...

BACKGROUND The Atlantic horseshoe crab, Limulus polyphemus, is valuable to fishing and biomedical industries, for education in public aquaria, and of ecological importance because the eggs provide a critical food source for migratory shorebirds. While hematologic and biochemical analyses are fundamental tools for health assessment, reports are limited for the four extant species of horseshoe crabs; L polyphemus (East Coast North America), Carcinoscorpius rotundicauda (mangrove horseshoe crab Southeast Asia), Tachypleus gigas, and Tachypleus tridentatus (Southeast and East Asia). OBJECTIVES This prospective study measured hemolymph values to determine RIs from free-ranging horseshoe crabs during the annual breeding aggregation in Delaware Bay, USA. METHODS Near-shore animals were briefly manually restrained for hemolymph collection from the cardiac sinus. Hematologic samples (25 males, 25 females) were collected for hemocytometer counts using the Natt and Herrick method. A second set of 50 animals (25 males, 25 females) was sampled for biochemistry measurands, including copper concentration by spectrophotometer, osmolality by vapor pressure osmometer, and protein electrophoresis. RESULTS Total hemocyte counts varied widely (RI 6600-44 300/µL). Electrolytes were consistent with osmoconformers living in seawater. There was a marked difference in sexes, with females showing much lower protein, glucose, and copper levels. Eleven females had multiple outliers, and all data were excluded from RI calculations. CONCLUSIONS Further studies of this species outside of spawning season are needed. Expanding our knowledge of horseshoe crab health is important to decreasing morbidity and mortality in research applications and maximizing longevity and overall health in display settings.

lbgBackground and Objective:l/bg Horseshoe crabs are widely used in both traditional and modern pharmaceutical applications. Most of the previous studies on horseshoe crabs focused on their blood which contains hemolymph and amoebocyte lysate. This study aimed to determine the potential antibacterial and antifouling properties of different extracts from the carapace and the book gills of ligCarcinoscorpius rotundicaudal/ig. lbgMaterials and Methods:l/bg The crude extracts were subjected to the bioactivity tests using the disc-diffusion and the inhibition of biofilm-formation measurement assays, for both the antibacterial and antifouling activities respectively. lbgResults:l/bg The results obtained indicated that the carapace extracts had stronger antibacterial and antifouling effects compared to the book gills extracts. Extracts obtained from the male displayed more activity compared to the extracts from the female with a few exceptions. Methanol and acetone carapace crude extracts showed the best overall performance. A sterol compound was isolated from the carapace acetone extracts of the male of ligC. rotundicaudal/ig. However, the compound did not display strong activity compared to the crude extract. The compound might be contributing to the observed activity with other components through a synergistic effect. lbgConclusion:l/bg The presence of antibacterial and antifouling activities in the carapace and book gills extracts could be added to the complexity of the defence mechanisms of horseshoe crabs. The results of this study, therefore, may contribute to the knowledge of the defence mechanisms of ligC. rotundicaudal/ig. Further research is needed to determine the bioactivities of other parts of the animal and to explore their potential applications.

The mangrove horseshoe crab, Carcinoscorpius rotundicauda, has divergent populations between the east and west coasts of Peninsular Malaysia, with the southern coast acting as a land barrier. The actual position of such a genetic break along Peninsular Malaysia as well as the connectivity status of the southernmost C. rotundicauda populations with east and west coast populations remain unexplored, however. The aim was to investigate the genetic diversity and structure of C. rotundicauda populations from the west (Kuala Sepetang in State Perak), east (Balok in State Pahang), and southern (Pendas in State Johor) coasts of Peninsular Malaysia. Haemolymph samples from adult C. rotundicauda specimens (n = 152) and eggs from their freshly deposited nests (n = 190) were collected monthly (from January 2016 to January 2017) for the sequencing of mitochondrial cytochrome c oxidase subunit I (COI). Gene isolates of C. rotundicauda from the present study were compared with National Center for Biotechnology Information (NCBI) GenBank sequences to cover most of the range of the species in Asia. A neighbour-joining tree strongly supported two clades, separating the west-coast populations from the south- and east-coast populations, with further substructure patterns. Both haplotype network and barrier analyses revealed a genetic break within the Strait of Malacca instead of the southern tip of Peninsular Malaysia. The southernmost samples from the Strait of Johor formed a haplotypic diverse gene pool that appeared only as a subclade of the eastern populations. In a detailed haplotype network of 347 individuals, individuals with similar COI sequences indicate connectivity between C. rotundicauda on the east and C. rotundicauda on south and south west of Peninsular Malaysia. Overall, the genetic break between C. rotundicauda populations is better explained by the convergent ocean currents and available mangrove habitats on the west coast (i.e. Strait of Malacca), rather than the point of the Malay Peninsula acting as a land barrier alone.

This paper reports on the complete mitochondrial (mt) genome of a horseshoe crab, Tachypleus gigas (T. gigas), in Kuala Kemaman, Terengganu, Malaysia. Whole-genome sequencing of hemocyte DNA was performed with Illumina HiSeq system and the generated reads were de novo assembled with ABySS 2.1.5 and reassembled using mitoZ against Carcinoscorpius rotundicauda and Limulus polyphemus, resulting in a contig of 15 Kb. Phylogenetic analysis of the assembled mt genome suggests that the Tachypleus gigas is closely related to Tachypleus tridentatus than to Carcinoscorpius rotundicauda.

Horseshoe crabs (Tachypleus tridentatus) are arthropods that restrict their distributions to natal vicinities. Briefly, shore perturbation from boating (Kudat), electric, cyanide and bombing (Kunak) and tourism (Semporna) in Sabah can impair the T. tridentatus growth and produce sexually mature adults with unusual size. The 8-point morphometry of Tachypleus tridentatus from Kudat (Sulu Sea), Kunak and Semporna (Celebes Sea), produces the final output constituting accurate size classification for the species. Meanwhile, T. tridentatus are sexually dimorphic (p = 0.968-0.989), where male T. tridentatus (from Kudat) has prosoma width (27.75 ± 2.68 cm) and weight (1050 ± 610 g) in smaller ranges when compared to the female (33.27 ± 4.68 cm; 3020 ± 1480 g) using the same comparison. In addition, the T. tridentatus populations from Kunak (prosoma width: male = 28.91 ± 1.48 cm, female = 29.44 ± 5.47 cm; weight: male = 800 ± 275 g; female = 2550 ± 155 g) and Semporna (prosoma width: male = 21.73 ± 1.34 cm, female = 24.42 ± 1.36 cm; weight: male = 485 ± 306 g, female = 1320 ± 640 g) differed site-wise. The descriptive statistics (average and standard deviation) relate 7.1-23.0% of T. tridentatus with negative size class. However, the applied statistics using stepwise analysis and regression curve (r2 = 0.566-0.833), relates 30.4% of T. tridentatus with negative size class. Considering weight to produce 100 % T. tridentatus with positive size class, it is biased because some crabs are gravid with eggs and if attained unpaired (male and female), they may have recently fed. Therefore, the prosoma (male), interorbit (female) and telson lengths are identified as most appropriate for the size classification of T. tridentatus. Thus, the findings provide a novel baseline for conservation studies that monitor symmetrical and unusual growth in the T. Tridentatus wild stocks.

In order to effectively manage a fishery, it is important to know the essential habitats used by all life history stages of the species being managed. However, this is often a challenge for animals such as the American horseshoe crab Limulus polyphemus, whose juvenile stages are difficult to find and quantify. Visual surveys and suction sampling have been used in previous studies, but in the Great Bay Estuary, New Hampshire, they are less effective, and so little is known about the habitats occupied by juvenile horseshoe crabs in this area. To fill this knowledge gap, we used SCUBA-dive surveys to locate juvenile horseshoe crabs. We found them on subtidal and some intertidal mudflats in the upper regions of the estuary, both adjacent to, and at some distance from, known spawning beaches. However we did not find them in either intertidal or subtidal areas adjacent to spawning beaches just 1-2 km closer to the coast. These data should be useful for future conservation efforts designed to protect essential horseshoe crab habitats in the Great Bay and other similar estuaries.

This study was conducted to investigate proximate content of horseshoe crab (Tachypleusgigas) in Malaysia. To date, there has been little agreement on what the nutrition value of horseshoe crab is and how it will benefit the consumers. The samples were divided by two parts, which are roe and muscle. The Tachypleusgigas was cleaned of foreign materials and impurities manually by human hand. The samples were ground into flour and sieved through 50 μm sieve and were packaged in airtight plastic bags prior to analyses. The horseshoe crab was analyzed for its proximate composition of different body parts. The results showed that the roe and muscle of Tachypleusgigas contained moisture (50.45 % and 73.67 %), ash (0.41 % and 2.72 %), crude proteins (38.24 % and 14.62 %), crude fats (9.30 % and 8.09 %), carbohydrates (1.67 % and 0.91 %) and energy (241.42 Kcal/100 g and 134.43 Kcal/100 g), respectively. This shows that roe has better nutrition content since it has higher protein, fat and carbohydrate content, which are the main energy-providing nutrient. Overall, the proximate content of Tachypleusgigas was nearer to the shellfish rather than the finfish and can be considered as a good nutrition source.

Species distribution models are used to predict ideal grounds, species range, and spatial shifts in an ecology over a span of time. With an aim to use Maximum entropy model (MaxEnt), presence records and pseudo-absence points are used to predict the Tachypleus gigas spawning activity for 2030 and 2050 in northeast India. The bearings of sixty T. gigas spawning grounds identified in 2018 were inserted into ArcGIS v.10.1. Meanwhile, 19 environment variables were inserted into MaxEnt v. 3.3.3, before the model performance was tested using receiver operational characteristics and area under curve (AUC). With an AUC of 0.978,85% was achieved for isothermality (bio3) and 74% for temperature (x= average) of the wettest quarter (bio8), all of which were inserted into ArcGIS to produce spatial maps. Although we learnt that T. gigas are still spawning in Odisha in 2030 and 2050, their distribution range is predicted to shrink due to the coastal morphology change. The climate conditions in Odisha revolve with the monsoon, summer and winter seasons from which, temperature variations do not only influence the annual absence/presence of spawning adults but also, the survival of juveniles in natal beaches. The use of MaxEnt offers novelty to predict population sustainability of arthropods characterized by oviparous spawning (horseshoe crabs, turtles, terrapins and crocodiles) through which, the government of India can take advantage of the present data to initiate the coastal rehabilitation measures to preserve their spawning grounds.